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University of Florida marine ecologist Mike Gil traveled from California to Hawaii on the SSV Robert C. Seamans with the <a href="http://www.sea.edu/">Sea Education Association</a>, the group responsible for the 2012 plastics expedition. The crew picked up large pieces of plastic debris that support life. (Mike Gil -- University of Florida)

Gooseneck barnacles colonize the mostly submerged portion of a red buoy fished out of the Pacific. (Mike Gil -- University of Florida)

Marine critters make a drifting home out of a hunk of yellow foam insulation. (Patricia Keoughan -- Contributed)

A smooth plastic toy ball supports a few barnacles, as well as a couple crabs. (Mike Gil -- University of Florida)

A floating fridge may have been part of the 1.5 million tons of debris swept into the ocean after the 2011 Tohoku earthquake and tsunami. Researchers found packaged food with Japanese labels inside. (Jonathan Waterman -- Contributed)

SANTA CRUZ >> Marine critters have trouble living on the smooth, slippery pieces of plastic bobbing in the ocean. Barnacles help give them a foothold.

But that could be a problem. Colonized plastic can carry marine life thousands of miles, potentially adding to the invasive species that already infect the Monterey Bay National Marine Sanctuary.

A new study reveals that gooseneck barnacles can transform marine plastic debris into floating islands of life. In 2012, Mike Gil, a marine ecologist at the University of Florida, sailed from California to Hawaii to collect plastic and see who had made it a home.

A torrent of plastic flows into the ocean. Scientists estimate 8 million tons wash into the sea globally each year. But the researchers think much of their plastic may have come from Japan. The country’s devastating Tohoku earthquake and tsunami in 2011 swept more than a million tons of debris into the ocean, and several items the ship’s crew found had Japanese writing.

Gil and the crew captured 31 plastic pieces, ranging in size from a few inches to about 5 feet long. With a dip net, they fished out bottles, buoys, foam insulation and plastic siding.

To figure out the abundance and diversity of life on each plastic piece, Gil denuded it of its colonizers. He picked off the crawling animals, such as crabs and isopods, which are crustaceans that look like backyard pill bugs. And with a knife, he scraped off the creatures stuck to the plastic, including the barnacles.

LIVING RAFTS

The study found that the more stationary barnacles on the plastic, the more other mobile species thrived with them.

That could be because barnacles glom onto the plastic by long, slimy brown stalks.

“You can think of them as trees in a forest,” Gil said.

The trunklike stalks provide more living space for other animals, as well as shelter.

“That’s where we found all the crabs and crawly critters,” Gil said. “Generally, they’re nestled among the bases of the stalks.”

Gil found that the plastic debris could even act like an upside-down reef, providing shelter and food for the reef-dwellers triggerfish and damselfish.

But these plastic rafts pose a potential threat to local ecosystems and economies, Gil said. They can transport flora and fauna from opposite sides of the Pacific. Just off the San Diego coast, Gil found a crab from Asia and an isopod from the Americas living on the same plastic.

Hitchhikers such as the foreign crab can potentially wreak havoc in a new habitat. Unlike in their native habitat, they may lack competitors or predators that would keep their numbers in check.

Natural rafts, such as downed trees or seaweed, don’t pose the same danger. They sink after days or weeks, whereas plastic can stay afloat for months or years, Gil said.

Researchers still don’t know how organisms from different parts of the ocean are bunking together on these plastic pieces. But Martin Thiel, a marine ecologist at Catholic University of the North in Chile, suspects it happens when different masses of water collide at what’s called a convergent front. The head-butting waters drag each other down, but whatever floats, including plastic, collects on the front’s surface.

“This is probably where organisms can jump from one floating thing to another,” said Thiel, who wasn’t involved in the project.

INVASIVE PROBLEM

Experts are deeply concerned abut foreign species invasions in local waters such as San Francisco Bay, the Monterey sanctuary and the Elkhorn Slough National Estuarine Research Reserve. With more than 230 non-native species, the San Francisco Bay estuary is one of the most invaded in world, according to the National Oceanic and Atmospheric Administration. The Monterey sanctuary, which stretches from just north of the Golden Gate Bridge to Cambria, has more than 40 exotic species.

Once invasive species become established, “it’s virtually impossible to remove them,” said Kerstin Wasson, research coordinator at the Elkhorn Slough reserve.

Invasive species aren’t like plant weeds you can spray with pesticides, she said.

“We encourage anyone who frequents coastal habitats to send in photos of any unusual species they see that don’t look familiar.”

Regulations try to stem the introduction of foreign species, but they’re difficult to enforce, said Steve Lonhart, a NOAA marine ecologist who monitors the Monterey sanctuary. For example, ships typically have filled their tanks with ballast water at one coast, and dumped it at their destination. That plops any living stowaways into a new environment.

But ships are now supposed to exchange the ballast water in the open ocean. It’s a desert compared to the rich waters of the coast, so it’s far less likely to have potentially invasive species, Lonhart said.

“But we don’t have an army of people and technology that’s checking every single boat that comes in and whether it’s adhering to the policies and protocols,” Lonhart said.

The plastics rafts heighten the risk of a biological invasion. In the long-term, the best way to counteract that risk is to curb plastic production, Gil said.

“And the only way to do that as a society is to reduce our dependencies on plastics in our day-to-day lives.”